1. Field of the Invention
Example embodiments of the present invention relate generally to load balancing transmission over a backhaul on the reverse link of a wireless communications network.
2. Description of the Related Art
FIG. 1 illustrates a general architecture of a well-known wireless communication network. In particular, FIG. 1 illustrates a portion of an EVDO wireless network. As shown, an access terminal (AT) 10 communicates with a base transceiver station (BTS) 12 over an air interface. Examples of an AT include a mobile station, a mobile unit, a wireless phone, wireless equipped PDA or computer, etc. Multiple base transceiver stations 12 communicate with a radio network controller (RNC) 14, which provides signaling and traffic processing for each wireless data session. The AT 10, BTS 12, RNC 14, and the interfaces between these components form what is known as a radio access network (RAN). The RAN communicates with a core network to access, for example, the internet. In the example of FIG. 1, the core network includes one or more packet data service nodes (PDSNs) 16 connected between the RNCs 14 and, for example, the internet (not shown).
The interface 18 between the BTS 12 and the RNC 14 is often called the backhaul. In particular, the interface 18 typically includes multiple T1/E1 lines connected between the BTS 12 and the RNC 14 for carrying packet data (e.g., IP packet data) between the BTS 12 and the RNC 14. Packet data flowing from the BTS 12 to the RNC 14 is said to flow over the reverse link, and packet data flowing from the RNC 14 to the BTS 12 is said to flow over the forward link.
FIG. 2 illustrates a portion of a conventional BTS. As shown, the BTS includes an IP stack 122, a plurality of IP over high data layer control (IPOH) interfaces 124, a plurality of physical channel interfaces (PHYs) 126, a management plane entity (MPE) 128, and an error detector 130. The MPE 128, the IPOH interfaces 124 and the IP stack 122 are logical elements implemented in processor of the BTS. The PHYs 126 are hardware interfaces, which each interface with a respective one of the T1/E1 lines. In EVDO, the physical channel interface is a TDMA PHY.
The MPE 128 configures each IPOH interface 124—protocols run at the IPOH interface 124, etc. As part of the configuration, each IPOH interface 124 obtains an associated IP address. Each IPOH interface 124 is associated with a respective one of the PHYs 126, and configures the associated PHY 126. For example, the IPOH interface 124 configures the layer 2 protocol used by the associated PHY 126. For example, the PHYs 126 may be configured to use the high data layer control (HDLC) protocol at layer 2.
Packets destined to the RNC 14 are received at an IP stack 122. The received packets may be data packets received by the BTS 12 from the AT 10. These packets are often referred to as user traffic packets. The received packets may also be data packets generated by the BTS 12 for control/management/signaling purposes. These packets are often referred to as interface packets. For example, a ping may be a form of interface packet. The interface packets will include a destination IP address that matches the IP address for one of the IPOH interfaces 124. By contrast, the user traffic packets do not have IP addresses matching an IP address of the IPOH interfaces 124.
During operation, the IP stack 122 examines header information in the IP packet to determine the IP address. If the IP address matches one of the IPOH interfaces 124, the packet is an interface packet and is sent to that IPOH interface 124. The IPOH interface 124 then sends the interface packet to the associated PHY 126.
If the IP address does not match the IP address for one of the IPOH interfaces 124, the packet is a user traffic packet. In configuring the IPOH interfaces 124, the MPE 128 establishes a default route from the IP stack 122 to one of the IPOH interfaces 124 for packets having IP addresses that do not match the IP addresses of the IPOH interfaces 124. Accordingly, user traffic packets are directed to a same IPOH interface 124. Consequently, the traffic packets for users are sent on the reverse link over a same single PHY 126. Unfortunately, it is expected that wireless communication systems will evolve to the point where a single T1/E1 can not handle a single user's reverse link traffic.
As mentioned above, the BTS 12 also includes an error detector 130 that detects physical layer problems. Numerous well-known techniques exist for detecting physical layer problems (e.g., a break in a T1/E1 line). The error detector 130 reports detected errors to the MPE 128. Similarly, the IPOH interfaces 124 detect layer 2 problems, and may report a detected error to the MPE 128. The MPE 128 disables the IPOH interface 124 associated a physical layer problem from communicating packets to the associated PHY 126, and therefore, the PHY 126 associated with the disabled IPOH interface 124 is disabled from communicating packets as well. An IPOH interface 124 detecting a layer 2 problem also disables communication of further packets. If a disabled IPOH interface 124 is the default route IPOH interface 124, the MPE 128 reconfigures the default route to a different IPOH interface 124. Upon recovery from the physical layer or layer 2 problem, the IPOH interface 124 may be re-enabled to communicate packets to the PHY 126.